#include <stdio.h>

int main()
{
	int a[30]={1,1,2,3};
	for(int i=2;i<=29;i++){
		a[i]=a[i-1]+a[i-2];
	}
	int s;
	scanf("%d",&s);

	printf("%d",a[s-1]);
	
	return 0;
}
